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How does an ARTCC achieve radio coverage of its entire region?
I live close to the edge of the ARTCC region covering my area. There is no way I could talk on VHF to the control center at normal GA altitudes; it might be possible from airliner or bizjet cruise altitudes, but I'm not sure even in that case. How do pilots who are outside radio range talk to ARTCC?

So their radio has coverage of at least their entire geographic area?

I can't talk on VHF ham radio to some 1/10th of the distance to ARTCC.

"How do pilots..." implies that aircrew have some ability to influence effective range.  Maybe better to rephrase to ask how the network of transmitters ensures full coverage in all sectors of ARTCC responsibility.

and your HAM radio may not even be capable of tuning the aviation band frequencies. ATC and aircrew don't generally like kids on the ground busting in and starting to chat...

Also, ham radio is ground-to-ground communication (usually). Aviation comms are air-to-ground, which increases the effective range dramatically.

@jwenting no, I was talking about ham-to-ham contacts on 2 meters, which is close to the airband.

@randomhead for airliners that might help, but from a few thousand feet, it's still unlikely that you could reach the ARTCC control center from here.

In an ARTCC, there are multiple sectors controlling their own unique slice of airspace. Each sector will have at least one frequency. If the ARTCC has 40 sectors, it will have at least 40 individual frequencies. When the controller transmits, his/her voice is digitized and sent over data lines to a Remote Communications Air to Ground (RCAG) site (commonly called a rag site) that is located in or near the overlying sector's airspace. When pilots transmit to ATC, the process is reversed, resulting in an analog voice in the controller's headset. All ARTCC frequencies go through a rigorous analysis to ensure the frequency coverage matches the sector's lateral and vertical limits.
If all sectors in an ARTCC are open, the frequency or frequencies assigned to a sector are used only for aircraft in that sector. As traffic volume is reduced, sectors can be combined so that one controller is using two or more frequencies. Aircraft will hear the transmissions of the controller to aircraft in a different sector, but will not hear the responding transmission from the aircraft since it is on a different frequency. On the midnight shift, it is not uncommon to have 3 or more sectors combined, along with their assigned frequencies.
Although every sector will have at least one dedicated frequency, the voice switch allows assigning different frequencies to sectors that would not normally use them. Usually this is done in response to a frequency outage. There are also discrete frequencies used for military operations in special use airspace. Additionally, all sectors have access to guard frequency (121.5/243.0) to communicate with aircraft that are in distress or have lost radio contact.

A  chum who used to fly across the border into the US from Canada (Cornwall Ont, near Massena NY) told me he was required to contact Boston Center before flying across, and to do that he had to climb several thousand feet to get LOS.  Maybe ten years ago. Dunno how it works now.

Remote Communications Air to Ground (RCAG) site that is located in or near the overlying sector's airspace — copying this for emphasis @Someone. The actual radio antennas are geographically diverse and may be nowhere near the physical ARTCC building. It may in fact be true that even an airliner on one side on the side of the Center's airspace would be unable to communicate on a frequency used on the other side of the airspace.

Most ARTCC RCAG sites are co-located with other FAA equipment, such as VORs, radar sites, and air traffic control facilities. This allows for maintenance personnel to be able to service multiple pieces of equipment without having to travel as much.

And to add some context to @RetiredATC 's excellent answer, a typical ARTCC will have 50 to more than 100 of these remote transceivers.  The number of transceivers needed for a geographic area is (a) the nature of the terrain and geographic size of the center's airspace, and (b) the traffic density.    You can only support so many concurrent conversations on a single frequency, so transceivers can be spaced more closely together in areas traffic volume dictates more frequencies be available.

ARTCCs don't have just one transmitter. Each one has multiple stations, connected to the central hub via wire, microwave links, fiber optics, etc. This is also why each center has multiple frequencies, because adjacent stations can't be on the same frequency or there will be interference, even if both stations are transmitting the exact same thing.

That makes sense! Is the same thing transmitted over all of the stations, or are they separately controlled?

@Someone In general, it's usually the case that the same thing is transmitted over all stations. I'm sure it's possible to isolate one station and use it individually, but most controllers usually don't bother.

@HiddenWindshield This would almost never be the case.  A center could easily be managing hundreds, and quite often thousands of simultaneously flights, with easily 50 or more controller stations operating 50 or more sectors through 100-200 distinct transmitters.  Any given transmitter has one and only one controller talking on it, and only aircraft in that controller's sector under that individual controller's supervision would be on that frequency.  It would be mathematically impossible to manage air traffic if transmissions for 500-1000 aircraft were "simulcast" on every frequency.


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Can you disassemble a plane, then rebuild it, and register it as experimental amateur-built?
Could I buy a Cessna 172 or a similar plane, take it apart into as many pieces as I safely could without damaging it, rebuild it, and register it as amateur-built? Assume that I know what I'm doing but do not have an A&P certificate.

What would be the purpose?  For what it's worth, you can register a certified aircraft as experimental with no disassembly required.  Equipment manufacturers do this to enable installation and testing of equipment for the purpose of getting approval of a Supplemental Type Certificate to add parts to certified aircraft.

@MichaelHall I was thinking of a case where someone wanted to make modifications without an STC. I didn't realize that was possible; the fact that you can register a certified aircraft as experimental without disassembling it makes this question moot.

Are you referring to yourself in the third person?  ;)

@MichaelHall possibly in the distant future; I don't expect to be able to afford flight training, let alone buying my own airplane, for a long time

One potential benefit of an experimental amateur-built airworthiness certificate is that the builder can sign off on the annual by getting a repairman certificate. If it is registered as experimental but not amateur-built, an A&P will have to sign off on it. Depending on the scope of the changes it may be difficult to find an A&P willing to sign off.

@MichaelHall While you are correct that you can convert a standard Type Certificate to an experimental certificate, Experimental-Amateur Built is not one of them. The other variations of experimental certificates come with very restrictive operating limitations such that you can't use it for any practical use outside of the certificates stated purpose. Having worked for a company with several experimental a/c; I can say, while they were essential to the business, the bureaucracy associated with them was a major nuisance.

@Gerry, good points, and I agree.  I just mentioned it as a FYI because my current company does this.

And if you replace lots of parts every time you take it apart/rebuild: Airplane of Theseus

The criteria to receive an experimental amateur-built airworthiness certificate are in §21.191(g):

aircraft the major portion of which has been fabricated and assembled by persons who undertook the construction project solely for their own education or recreation

The "major portion" in this case meaning more than 50%.
In your hypothetical situation, you did zero percent of the fabrication. Arguably you also did zero percent of the assembly since the plane was already fully assembled when you got it. But in any case even if you fully disassembled it into its constituent parts there is no way you could possibly do more than 50% of the assembly work.
I imagine you would also have a hard time convincing the FAA that you were doing this "solely for your own education or recreation" and not to exploit some legal loophole regarding experimental aircraft.

Disassembling and rebuilding something may well be educative and entertaining!

Indeed! Still, you need to convince the FAA that that's your only reason for doing it.

Yes, I wasn't trying to make a legal argument, just a trivial remark! :)

In North America, you have to complete more than 50% of the construction yourself. In the case of a project like that, you'd have to negotiate with your local authority to agree on activities that constitute 51%.
Stripping it down and overhauling it doesn't count. You could however, build new wings from scratch and use an existing fuselage, and your local authority might agree to that as amateur built. Or replacement of a significant amount of the skins or other major structural repairs might do it. So a rebuild of a wreck might meet the requirement.
On tube and fabric airplanes, stripping it down the the bare tubing, and rebuilding a significant part of the wings, like new spars etc. might be enough to satisfy a 51% requirement. Something that replicates a "quick build kit" more or less. There are plenty of amateur built Champ or Piper Pacer rebuilds that are like that.
In Canada, there is a category called "Owner Maintenance" that you can reregister any airplane on an approved list into, and it becomes similar to amateur built. You can rebuild an OM airplane as much as you want, use non-certified parts, etc. The only requirement is the owner has to have a pilot's license.
The catch is, you can't fly it outside Canada, you can't use it for IFR operations, and you have to X out all the serial numbered components so they can never be used in a certified aircraft again. It's a bit of a one-way road. There was a guy who registered a Sea Bee in OM, and put a Corvette V8 engine conversion in it some years back.
You can put a Cessna 172 or a Cardinal into OM category, but it's not done very often because of the limitations placed on the airplane. It tends to be limited to airplanes that are never likely to cross the border. In fact, because the US has no such category and doesn't recognize OM, you can't even overfly US territory with your OM airplane.

"In North America, you have to complete more than 50% of the construction yourself." From recent articles about Murphy Aircraft which are based in Canada I gather that the 50% rule only exists in the US. Also, remember that 50% does not apply to the amount of work, but rather to the number of different tasks. That's how builder assist programs work: you cut one blank, you form one rib, you set one rivet, etc. and the company employees do the rest for you.

The rules in Canada are broadly similar WRT 51%. Except there is an inspection requirement during construction of a homebuilt. Also, Canada has no "repairman certificate" requirement. Whomever's name is on the C of R of a Cdn homebuilt can sign off all maint repairs and overhauls.

Mmh, funny. Maybe some misunderstanding, I based my comment on this and this Kitplanes articles, both published this year.

Transport Canada waives the 51% part for certain kits. There is a list. https://www.md-ra.com/en/faq_en.html  Outside the list of fast build kits approved, the 51% still applies.

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What are "CIRCLING CATS"?
A NOTAM at Pensacola International Airport (KPNS) uses the phrase "CIRCLING CATS". What does this phrase mean?

This question will be far easier to answer, and the answers more meaningful, if you can give an example of a NOTAM where this verbiage appears. Not because what you're asking is obscure (it isn't), but because answers will seem abstract without more context in the question. The How do I ask a good question thread recommends specific questions with details and context. Adding those will improve this question.

This answer will provide some background.

Highly correlated to circling mice. ;

A circling approach is one where you line up on one runway for the approach through the clouds, but once you break out of the clouds you circle around and land on a different runway due to winds.  This will happen when the runway favored by the winds does not have a published instrument approach procedure.
Aircraft are grouped into different approach categories based on their final approach speed.
I haven't heard the specific term "circling cats" before, generally what you would hear instead is "circling mins".  In other words, the minimum altitude you would fly the instrument approach down to before either expecting to see the airport and be able to land, or be expected to execute a missed approach procedure.
The minimum altitude would vary by approach category because a faster aircraft will have a larger turn radius during the circling portion of the approach, therefore they will need to be a bit higher to ensure terrain clearance.
If you happen to find the complete NOTAM please post it, I may be able to give a better answer with some context.

Seems to me that "circling cat" world refer to the approach category of the aircraft, but I guess we aren't certain.

@randomhead MichaelHall, the NOTAM that 757toga quoted is the one I saw.

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Are distress calls used in simulators?
Would a pilot flying in a flight simulator with VATSIM make a mayday call in a scenario in which a pilot in a real plane would?

Why wouldn't he? A flight simulator is a procedural trainer. A mayday call is as much a part of an emergency procedure as anything else he might practice.

@AdityaSharma oops, VATSIM. Autoincorrect "fixed" it for me.

You would get a better answer asking a forum of VATSIM users. This site is generally for real-life aviation; asking what people do in their hobby at home is not really on topic here IMO.

@Ben well, it's like your opinion man. I am a PPL student, and VATSIM+MSFS helps me a lot. For instance, in preparing for those emergency calls I certainly hope I will never have to make IRW. Besides, OP did not mention he/she is using the sim as a hobby. Simulators are very much used in the industry, and certainly not for gaming...

@CTZStef I'm not denying that home simulators, when used properly, can be helpful for training, but the majority of its users are hobbyists. Asking "what do people do on VATSIM?" is much better asked on a forum dedicated to VATSIM or at least online gaming.

In a real Level D simulator, you perform for the instructor as it it was real life and that includes radio calls. Unless the instructor tells you not to bother.
For VATSIM, you should go on the controller's VATSIM discussion board and ask if emergencies are encouraged. Some of the controllers on VATSIM are real life controllers and would probably enjoy the change of pace, and so would most of the other flight sim participants for that matter.  But I would check with the community first.

What if someone is flying a simulator for practice without an instructor? I was thinking of people running FlightGear, X-Plane, or a similar program on a home computer too, not just commercial training simulators.

@Someone, Nobody can answer for what an individual at home might do...

@someone I'm going to suggest that the bigger question if working in a multi user environment like VATSIM, should you even have faults etc turned on? Messing with someone else's practice by showing up and calling emergency is potentially very antisocial. Would suggest it only be done with prior discussion to whoever is running ATC at the time, and do not know enough about the online systems to say how to do that.


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Is more information available about missionary pilot Nate Saint's backup fuel system described in "Through Gates of Splendor"?
I'm currently reading the book Through Gates of Splendor, and at one point (pages 61-63 in the first edition, about halfway through Chapter 5), it describes a system invented by missionary pilot Nate Saint that provided a backup to the main fuel system in the Piper PA-14 Family Cruiser that he was using for missions flights. Because the book is not primarily about aviation, it doesn't go into a lot of detail on how the system works. The system was designed to protect against problems "such as clogged vents and broken lines."
Is there any more information available on it?
It apparently bypassed the entire fuel system, including the carburetor, and used fuel from an extra tank strapped under the left wing and made more aerodynamic with a balsa-wood fairing. Throttle was controlled separately, not by the plane's normal control, but he did add a control rod to the instrument panel; it appears that the rod simply opened and closed (or adjusted to partially-open settings) a valve. The system was able to function without a carburetor because the engine was still windmilling when it was started(?). (I didn't know a non-fuel-injected engine could run without a carburetor, but apparently it is possible if the engine is already spinning at a high enough speed?)
He flew to 2,000 feet on the normal system, then "pulled the mixture control to idle-cut-off" (I think that means he turned off all fuel supply to the engine?) and turned the handle he had added for the backup fuel valve. The engine "wound back up to a smooth full-power"; he flew with this system for twenty minutes. He said that it worked just as well as the primary fuel system.
The system weighed four pounds including the (empty) tank, and must have been quite simple because he built it with only the extra parts he had access to.
This system was installed in at least two other planes, because it says that all Mission Aviation Fellowship "now" use the system, and when this book was written, the original plane had already been destroyed. (I don't know if they still use the system; the book was published in 1957 and my copy appears to be the first edition.)

Need to find the source book to answer but have seen a similar system described for missionary operation in Papua New Guinea that was a hose gravity feed to a basic spray nozzle downstream of carburetor, manually tuned to run rich. Basic idea being to give the single engine aircraft at least enough power pick a better crash site. Suspect something made worth while by the high risk of dirty/contaminated fuel. It is an area with high carburetor icing risk but unclear if this system would actually help?

@GremlinWranger no, this was in Ecuador, so carb icing is very unlikely. Clogged fuel lines are one issue that was specifically mentioned.

@quietflyer yes, it was strapped under the left wing.

@quietflyer was it Jungle Pilot (https://www.amazon.com/Jungle-Pilot-Gripping-Martyred-Missionary/dp/1572930225)? If it was, I might get a copy and read it.

@Someone -- yeah I'm pretty much 100% sure that was the book, so have posted an answer.

Some relevant information exists in a book called "Jungle Pilot" by Russell Hitt (link to Amazon).  My recollection is that several pages were devoted to the subject.  The same book also gives some attention to a concept for a tri-motor bush plane that Saint was exploring / advocating.


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Can a person with cerebral palsy become a pilot?
I have mostly succeeded at everything I want in life except the one hobby I wish I could take up, and of course that hobby is flying, or I wouldn't be asking here.
Background
I graduated high school in 1995, and graduated college in 2003.  I'm nearly 50, and if I don't do this now, I may never.  I was born with Cerebral Palsy.  I wish I could say it affects everyone who has it the same, which would make this question easier to answer, but it affects people differently.  I'm what's known as a Spastic Tri-plegic (tight muscles affecting 3 limbs).  As such I have "no legs" that work, a right arm with control, but no fine motor control (I can use the arm but not the fingers).  The only limb hat works 100% is my left arm.
Impact
I realize the following will occur:

Rudder Control with Feet non-existent.
Yoke Control/ascent/descent possible.
Turning possible.
Throttle Control possible if on left.

I'm not wanting to go past General Aviation, but knowing the above, I'd like to ask the forum here if obtaining a Civilian Pilot's License is even possible  with modifications that would give me rudder control?
Thanks,

This isn't enough for an answer, but one important thing is to not apply for a medical certificate before having an appointment for a consultation (not an exam and application) with an experienced aviation medical examiner. If you have an exam and are denied a medical, your alternative routes will be significantly limited compared to the situation if you had never applied for a medical. If you've never applied, then you can fly as a sport pilot using only a driver license instead of a medical, but that is not an option if you have been denied a medical.

Yes, you can be trained as a pilot even if not all four of your limbs can be used to control an airplane.  Some examples:
Jessica Cox is licensed, despite having no arms.
Her type, the Ercoupe, may be the best known GA airplane with no rudder pedals.
Operating yoke and throttle with only right arm sounds mechanically simple enough.  That frees up the left hand to operate buttons and switches on radios and navigation equipment, but, even so, some (older) airplanes don't have those at all.
The FAA has published guidelines for evaluating pilots with CP, so this isn't unheard of.  Also in the UK.
Finally, in the USA at least, ultralights require no license, and often have few or no instruments to finger-operate.  Some even omit some control surfaces, simplifying one-arm control.  Weight-shift ultralights are even simpler to operate: no control surfaces at all, just a hang-glider-like "yoke."

I guess I should add to my question, but how do I find training, i.e., a flight school now that you've advised it is possible?

In the USA, start with the EAA.  They can guide you to trustworthy training for pretty much anything you'd be aiming for.  Happy hunting!


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Communicating one's ground position by sighting an overhead aircraft (M*A*S*H)
In an episode of the 1980's television show M*A*S*H, several of the characters are stranded in the wilderness when their vehicle breaks down.
In an attempt to communicate their position to any allies that might be listening, one of the characters says this into their walkie talkie:

Frank Burns: There is a fighter plane approaching. And, um, when I say "Now", the jet will be directly over my head.

[the jet whooshes overhead]

Frank Burns : Now!

The other characters think this is a useless effort:

B.J. : Frank, that thing is a thousand feet up going 500 miles an hour.

Hawkeye : By the time you said 'now', the plane was in its hangar and the pilot was in his jammies.

Was it actually useless?  I always thought it was a clever idea.
This is a complete layman's question.  I am not a pilot.  (But my Dad is, if that helps!)

If the jet really was doing 500 mph — about 225 meters per second — and it took Burns between five and 10 seconds to transmit “now”, and assuming the pilot heard his transmission, his position could be located within a square kilometer or so, an enormous help to any search party.
If the pilot did not hear the transmission but whoever did knew or could find the jet’s flight path, that would still narrow down the search area considerably.
I never liked M*A*S*H and the show’s treatment of Burns was one of the reasons.  The creators of the show clearly wanted to be taken seriously when it came to almost all aspects of military life in a war-zone — but felt it was better to keep Burns as the butt of jokes rather than investigate what could or should be done about a doctor who was (supposedly) inept or an officer who was (again, supposedly) unprepared for command.

" and it took Burns between five and 10 seconds to transmit “now”," this is a very questionable assumption, unless aviation radios are really hard to use. I could say one word on a ham radio in a second or two.

It depends, was he talking directly to the pilot?  If so it is reasonable as long as there were some geographical references the pilot could use to fix location and plot on a chart later after landing.  Also, some military navigation systems have a "mark" feature, allowing the pilot to hit a button and preserve that location as a lat/long in the system to recover later.

He wasn't talking to anyone specifically, just hoping that someone was listening.  Possibly no one at all.  I did not get the impression that he thought the pilot was listening.


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Why was the nose gear of Concorde located so far aft?
Was this because of the drooping nose preventing it from being placed anywhere further up?

I suspect your hunch is correct.  The nose gear on the concord retracts forward so the tire ends up almost underneath the "A" in the word "Air."  Any further forward and you'd be retracting the nose tires into a space that's (a) already shrinking because of the fuselage taper, and (b) competing for space with the nose mechanism.

Most airliners have the nose gear behind the cockpit, but it is more pronounced on the Concord.  Realize though that the main gear is proportionally further back as well, so likely the nose gear placement was decided on with some consideration to taxi turn radius.

In a conventional "tricycle arrangement", placement of the nose landing gears is normally chosen to respect three basic requirements:

nose landing gear should carry 10 to 15% of the total weight; a smaller value would imply less authority for steering while a bigger value would imply that the main landing gear is located too aft in respect to CG;
when braking, an additional load is downloaded on the nose landing gear due to the CG "pivoting" around the braked main landing gear; this has to be limited due to structural reason of the front tires;
the "overturn" angle $\theta$ as defined in the following picture¹ should be also limited to avoid overturn around sharp corners:

Obviously other non mechanical reasons might limit the landing gears placement but those three requirements should be respected anyway.
Just for comparison, an A321 has main landing gears 7.6m apart and a wheelbase of 16.9m. Concorde had 7.7m and 18.2m respectively, so actually quite a standard placement. Placing the nose gear farther in front would have reduced the weight distribution under the 10% of the previous point 1. and it would have reduced the manoeuvrability on the ground as given in 3.
I don't know the CG excursion of the Concorde, if somebody has a couple of numbers I'd be glad to do the math to show if (hopefully!) the nose gear placement respects those three requirements.

¹ from this paper, in turn from "Currey, N. S., “Aircraft Landing Gear Design: Principles and Practices,” AIAA Education Series"

Excellent diagrams.  Being a delta, the CG is further back.  Maybe it was the ground turning radius parameter that played a role in the design.

@RobertDiGiovanni, or they could have designed it to do a donut!  ;)

@MichaelHall: driiiiiift


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Why is this plane indicating an altitude of 117,200 feet?
Looking at a plane tracker, I found something where the altitude is crazy high. Could it be a plane masking identity?

There is an AEROSTAR up right now on boarder of Canada at 50,300 ft. What can go over 100,000 ft?

a bad altimeter setting can go over 100,000 feet. unfortunately the registration and ICAO codes are cut off in the screenshot, so it's hard to go back and see.

@tedder42 Registration could be SU-BAV, which is an Egyptian military C130. Would be nice if we had a timestamp though.

@Chris I've seen Egyptian AF C130s with this exact issue many times, so I think you're absolutely correct

As an aside, this is why ATC has to verify a plane's altitude.  When the pilot with good phraseology reports, "four thousand climbing one two thousand," (or the pilot with bad phraseology reports "four for twelve"), ATC correlates what the pilot said their altitude is ("four thousand") with what the plane's transponder is telling ATC's radar that the altitude is.  If they don't match, there's a chance the reported altitude is incorrect for some reason, as with the plane in your question.

@Fattie Uh, no. That is obviously an Android screenshot.

I guessed this was about the Egyptian C-130s just from the title. I've seen them flying into BWI with my own eyes while they're reporting these erroneous altitudes. Whatever the failure is, it's not just a one-off - it happens with multiple different aircraft.

@nobody - you're perfectly right, thanks.  I'm so used to pointing out the "overwhelming iFone screenshot issue" on SE sites, I didn't think. Thanks for pointing out my mistake

What flight tracker are you using?

Without knowing the details of the flight, it looks like one of the bits in the altitude transmission is set wrong. In the coding of altitiude, the transponder uses the so-called Gillham code. This is a modified Gray code which changes only one bit between successive values.
I suspect the D2 bit is driven by a cable which either has a loose connection or a break and is intermittently shorted to ground. In this specific case this would lead to an altitude of 8300 ft to be transmitted as 117200 ft.
The transponder sends altitude encoded in 12 bits, logically grouped in four groups of three bits: [D4,D2,D1] [A4,A2,A1], [B4,B2,B1] en [C4,C2,C1]. (The transmission sequence of bits is a different order then depicted). D4 is not used for altitude, 11 bits are sufficient.
8300 ft is coded as (0)00 011 010 100, with D2 being the bold (MSB) bit. 117200 ft is (0)10 011 010 100.

Interesting!, can you elaborate on how a short would cause an altitude of 8300 ft to become 117200 ft?

@ROIMaison 8300 ft is 000 1101 0100, with D2 being the leftmost (MSB) bit. 117200 ft is 100 1101 0100. The fact that the color coding of the track indicates jumps up and down makes me believe this is very likely correct answer. You can look more at gray codes on https://www.avionictools.com/graycalc.php

I've noticed this exact issue many times with Egyptian air force C130 flying over Europe, but I'm not sure if it's always the same aircraft.

Amazing domain knowledge !

I'm looking right now at SU-BKS doing the same thing intermittently so it's definitely not a specific-aircraft issue (maybe a manifacturing defect on the whole batch of transponders?). It's alternating between 104300ft and 21200ft, so it's again the leftmost bit that is changing

The altitude record for a subsonic fixed wing aircraft is 76,000 ft (Perlan II).
It is not possible that both the altitude and the ground speed are correct.  Lots of things fly at that ground speed.  Without knowing anything about the flight, it's quite probable the altitude is wrong.

Is there any possible way a C130 could be flying at 117,200 ft?

@Someone No.  Everything about the design is wrong.

What was wrong with my edit then?

@Someone  Edits really aren't intended to be used to wordsmith somebody else's answer. When there's a typo in a post, sure. When a link can be added or updated, great. When the originator isn't a native English speaker and an edit can improve the readability of a question or answer, then yes. But "improving" somebody's choice of words, not so much. Which is why the original author retains the ability to reject edits. When one disagrees with an answer's content, the way to register that is a down-vote. But Stack Exchange doesn't use edits (the way Wikipedia does) to correct another's work.

@RalphJ - just to clarify for those of us who are newer, I don't think you meant that it is out of line to have a different opinion on wording, but that if it changes meaning even slightly it is best to discuss it in the comments rather than editing. And downvoting if I understand correctly is for disagreeing with the entire premise of the answer not just disagreeing with some of the specific wording. The exception would be community wikis which have a different methodology. At least that's how I understand it.

@StevePemberton Yes, exactly.

I don't necessarily mind the edit as I am not a professional, just an enthusiast in aviation especially anything military related. If it helps bring in more professionals then go for it.

On a lighter note imagine if ground control wasn't aware of such failures. Uhhhhh, this is ground control to Pilot. Uh huhhhh, Chad was just joshing ya about how high he last took his C-130 this morning. This is not Spaceforce. Reduce altitude ASAP.


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Can you fly a VFR practice approach at night that is Notam’ed “NA at night”?
To frame the question more specifically, at KCSV the ILS Z 26 approach is NOTAMed “NA at night”. So is it legal to fly the approach VFR for training purposes to satisfy aeronautical experience requirements toward an instrument rating?
Or is the approach not authorized for flying under any conditions at night?

If you are flying VFR, can't you pretty much do whatever you want, so long as you don't violate any FARs?

That’s my thought as well, but I’ve been told by two other instructors that you can’t do it. I just can’t tell if there’s a real FAR reason behind that or if that’s just speculation or caution as it obviously is more dangerous as there are probably higher obstacles preventing the procedure from being used at night.

Oops, the VOR-A is the only approach at that airport that isn't NOTAMed NA at night, but it is NOTAMed "Procedure NA". So I fixed the question to be about ILS Z 26 so the question makes sense now. Though honestly the same question could apply to "Procedure NA".

@quietflyer You could probably fly it VFR (though it would be a bad idea), but counting it as a practice approach probably not.

The latest NOTAMs for KCSV indicate RWY 26 PAPI UNUSABLE until 10/08/2023, so that's probably why you shouldn't shoot VFR approaches at night. https://notams.aim.faa.gov/notamSearch/nsapp.html?METHOD=DISPLAYBYICAOS&REPORTTYPE=RAW&FORMATTYPE=DOMESTIC&RETRIEVELOCID=CSV&ACTIONTYPE=NOTAMRETRIEVALBYICAOS#/results

The IAP in question only takes place in class E and G airspace. So you can definitely "do" it in VFR, and you don't even have to talk to anybody.
Unless you know for a fact why it is not allowed at night and know that it doesn't apply to VFR flight for some reason, I would consider this to be reckless behavior. I expect if there were any issues the FAA would throw the book at you under 91.13. Assuming you survive the CFIT, anyway.
I could see an argument either way whether it would be legal to log this as an approach. I'm leaning towards "no," with the argument that a "not allowed" approach is essentially the same as no approach existing, from a legal standpoint.
But even if it is legal, you're putting evidence of having done something reckless in your logbook, which seems less than wise. (Not as unwise as doing the approach in the first place, mind you).

Legally yes, operating under VFR, it is possible to do this.  That being said, I would seriously think twice about doing so as there is a reason approaches are not authorized under certain conditions, mainly terrain hazards, and other risks, which would not be readily identifiable at night.  Ignoring this advice has killed people, such as this tragic Learjet crash out in El Cajon, California, on December 27, 2021.  The approach plate is listed below.

Note that circling to land on runway 27 right, and runway 35 is not authorized night. To get around this constraint, the Learjet pilot canceled IFR flight and went VFR, so he could attempt a circling maneuver to land.  San Diego has a lot of mountainous terrain to the north and east of the airfield. This in combination with marginal weather conditions at the time of landing, as well as poor management of airspeed during maneuvering led to a fatal accident.  There’s often very good reason why, when the area is surveyed by the FAA in the creation of that instrument approach, they did not authorize a circle to land or is other procedure during an approach.

IMHO, VFR flying is not actually possible at "night" which is defined in FAR 91 as 1 hour after sunset till one hour before sunrise. ((FAR 91 1.1.Night means the time between the end of evening civil twilight and the beginning of morning civil twilight, as published in the Air Almanac, converted to local time.)
BUT,
FAR/AIM 91.155 Basic VFR weather minimums. 155/b.(b) Class G Airspace. Notwithstanding the provisions of paragraph (a) of this section, the following operations may be conducted in Class G airspace below 1,200 feet above the surface:
(1) ...
(2) Airplane, .. If the visibility is less than 3 statute miles but not less than 1 statute mile during night hours and you are operating in an airport traffic pattern within 1/2 mile of the runway, you may operate an airplane, .. clear of clouds.
It seems that your answer is in FAR/AIM155/b. if VOR not available, and its darker night, I will treat the airfield as non-towered and remember to signal on CTAF traffic band for PCL to turn on the lights 3, 5 or 7 clicks on mike. If it's towered, I'll state my intentions and keep on the pattern for touch and go's as long as ATC allows it.

VFR flying is not actually possible at "night" -- well, the alternative is to file an IFR flightplan for every night flight. Opinion notwithstanding, I'm pretty sure that VFR at night is a very, very real thing in the U.S., which the question, tagged as FAA Regulations and referencing a Kxxx airport, is asking about.

Night VFR flights happen all the time in the US.


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Can You Transmit with Airband Transceiver
I am considering the purchase of two Dittel FSG-5 Airband (118-137 Mhz) transceivers. If I transmit from one radio to the other, and vice versa, am I breaking any rules or potentially causing an issue with pilot/ground crew transmissions?

One note: with radio, you never transmit from one device to another device. Your transmissions are sent into the void for anyone else to listen in on. (You may be able to encrypt your transmission but it will still be broadcast into the void.)

In which country would you use the equipment?

If you are not using them for aviation purposes or for an emergency, yes, you would be breaking the law, and yes, there is a significant possibility of interfering with aviation-related communications. This will apply in virtually any country.
If you do use them for aviation, and you are a pilot using a radio in an aircraft, then that should be legal. At least in the US, I do not believe any license is required other than your pilot certificate. In other aviation-related contexts, you may be able to obtain a license; I am not familiar with this process, but expect your use of the radios to be strictly regulated, if your license is granted at all.
If you just want personal communications, for non-aviation purposes, a service such as Family Radio Service (in the US) or PMR446 (in Europe and the UK) may be more suitable. Transceivers for these bands should be readily available from sites like Amazon, and possibly from some brick-and-mortar retailers.
Depending on laws in your jurisdiction, and the willingness of you and the other people to whom you want to talk to pay license fees, do some paperwork (or online forms), and possibly take some tests on radio theory and regulations, a licensed service such as General Mobile Radio Service (US-only) or amateur (ham) radio (available in almost all countries, but licensing procedures vary widely) may be an option.
One word of caution regarding amateur radio: many amateur transceivers are available on Amazon without being clearly marked as amateur radios. These include, but are not limited to, "Baofeng," "TYT," and "Radioddity" brand radios. Before purchasing a radio, check the laws in your country and make sure the radio is designed for use within a service that is available in your country, and that you have a license if one is required. Of course, if you have an amateur radio license, it is OK to use amateur transceivers as long as you follow the regulations.
Citizens' Band is available in many countries as well. In the US and many other countries, you do not need a license; in some others, a license is required.

Good Lord! It is what I feared, especially when you add in randomhead's kind comment, that the transmission from the TX device goes "into the void" as a public broadcast, much akin to CB transmissions. So, bottom line, having a pair of the devices is about as useful as a bathtub without a drain connected to it. Did I miss anything? Thanks for everyone's help, I'll stick with my Autophon and Stornophone UHF radios.

@GaryBrant FYI, that's true of any radio. Every bit of spectrum is allocated to specific uses. You need to make sure your transmissions are in a band that you are legally permitted to use.

Thanks, Chris. But one has to ask - where are the warnings about this subject from retailers like Amazon, that extoll ICOM and other makers aviation radios. I mean, if you're going to listen to chatter, innocent enough, why not just use a scanner?

@GaryBrant I don't know why warnings aren't posted, but it is a general thing that operating most radios requires a license. This applies to aviation radios as well as HF/VHF/UHF radios except in a few specific bands.

@GaryBrant what country are you in? I could add more details that will be relevant to your situation if I know what country you're in.

I'm a New Yorker, thank you for your help. Gary

Another quick question, I must assume the operator's location eg. how far you are from an airport is immaterial. In other words, a transmit might interfere with a plane flying overhead, within range of your radio. Is that about right? Thanks again, Gary Brant

@GaryBrant thank you! Since you're in the US, FRS sounds like the best option for you, or maybe GMRS or CB if you need more range. Being far from an airport makes interference less likely, but certainly does not eliminate the risk, and distance to an airport has no effect on legality.

"At least in the US, I do not believe any license is required", no licence for the US, but an  operator certificate.

@mins yes, it's required for international flights.

@GaryBrant no clue why anyone would use a transceiver rather than a pure receiver if they don't have any business transmitting. Of course if you have a transceiver anyway and are wanting to use it for reception only on occasion, why buy a receiver for those days only? Of course there might be laws prohibiting use outside of strictly defined parameters (like we have here, can't use a transceiver at all outside a licensed vehicle or location, and need a special license and permit for each one).


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What's this fuel line for?
Cessna 414 ram conversion

What's this fuel line for that is coming to injector, other then the one from fuel distributor?

It's a boost reference line which carries supercharged (Upper Deck) air to the injector for mixture atomization. Naturally aspirated engines don't need this as there is no positive pressure differential between intake manifold and the ambient atmosphere.


text:
Is a Class 2 medical enough for being a (remunerated) Flight Instructor (FI (A)) in the European Union (EASA)?
Suppose I only hold a valid PPL(A) License with a valid Class 2 medical certificate issued in the EU. Can I become a Flight Instructor for PPL(A) with this medical certificate or do I need to hold a Class 1 medical certificate?
As far as I understand it I do not need a Class 1 medical certificate, but please correct me if I am wrong.
From the EASA document below, you may either hold a CPL license hold at least a PPL(A) and have passed the CPL theoretical knowledge exam. Now, the CPL does require a Class 1 Medical certificate, but what about passing the CPL theoretical knowledge exam?
I am asking since, theoretically, with a PPL(A) you are not allowed to be paid for flying. Would then be being an instructor the only exception?
This document states the following requirements: (See SECTION 2: Specific requirements for the flight instructor — FI):

An applicant for an FI certificate shall:
(a) have passed a specific
pre-entry flight test with an FI qualified in accordance with  FCL.905.FI(j) within the 6 months preceding the start of the course,to assess their ability to undertake the course. This pre-entry flight test shall be based on the proficiency check for class and type ratings as set out in Appendix 9 to this Part;
(b) for FI(A) and FI(H):

have received at least 10 hours of instrument flight
instruction on the appropriate aircraft category, of which not more
than 5 hours may be instrument ground time in an FSTD;

have completed 20 hours of VFR cross-country flight on the appropriate aircraft category as PIC; and

(c) additionally, for the FI(A):

hold at least a CPL(A); or

hold at least a PPL(A) and have:
(i) passed the CPL theoretical knowledge exam, except for an FI(A) providing training for the LAPL(A) only; and
(ii) completed at least 200 hours of flight time on aeroplanes or TMGs, of which at least 150 hours shall be completed as PIC;

have completed at least 30 hours on single-engine piston powered aeroplanes of which at least 5 hours
shall have been completed during the 6 months preceding the pre-entry flight test set out in (a) above;

have completed a VFR cross-country flight as PIC, including a flight of at least 540 km (300 NM) in the course of which full stop landings at 2 different aerodromes shall be made.

I feel your pain, why do they make this so hard to understand?!

You can become a PPL(A) FI (without a CPL) with only a class 2 medical.
I did this, and I am the Chief Flying Instructor at an EASA ATO. We have employees who also do this.

FCL.205.A PPL(A) — Privileges
(a) The privileges of the holder of a PPL(A) are to act without
remuneration as PIC or co-pilot on aeroplanes or TMGs engaged in
non-commercial operations.
(b) Notwithstanding the paragraph above,
the holder of a PPL(A) with instructor or examiner privileges may
receive remuneration for: (1) the provision of flight instruction for
the LAPL(A) or PPL(A); So a PPL holder may give instruction.

FCL.040 Exercise of the privileges of licences  The exercise of the
privileges granted by a licence shall be dependent upon the validity
of the ratings contained therein, if applicable, and of the medical
certificate as appropriate to the privileges exercised. To Exercise
the privileges of a PPL you need a Class 2 Medical Certificate.


text:
What modifications need to be made on an engine that normally uses AVGAS to utilize it with MOGAS?
Asking just out of curiosity. What modifications need to be made on an engine, e.g. Lycoming O-360, that normally uses AVGAS to utilize it with MOGAS?

Just to confirm you mean just the engine itself, not the fuel delivery system, fuel tanks, or anything else on the airplane?

Yes, mean the engine itself.

I think you need to narrow this question down some, there are many, many engines out there and they aren't all the same. Some will require no modifications whatsoever, other may not be able to use it at all.

Might depend on the particular engine, but in the only example I'm familiar with (Lycoming O-360 in a Piper Cherokee) no engine modifications were needed, just the installation of dual electric fuel pumps replacing the OEM one.

STC aside, no physical modifications are required to an engine to run on Mogas (except possibly the fuel system - see below).  My Lycoming O-290 has been using it for 9 years with no issues, and in fact the engine is FAR happier on Mogas than 100 LL, which low compression engines are unable to lead scavenge adequately and require frequent plug cleaning and are prone to exhaust valve sticking from lead buildup on valve stems (on engines meant for 80 octane).
The only benefit to running an 80 octane engine on avgas is a lubrication benefit to valve seats due to oxidized compounds that form with leaded fuel, and I will put some avgas in from time to time (there is a sliding action on the valve seat as the valve centers itself when closing - the lubrication effect reduces seat wear from this sliding).
One interesting effect is when I borescope my cylinders at annual, the exhaust valves are uniform off-white like they are in car engines, from the ash deposits unique to Mogas (on avgas, exhaust valves have a reddish bullseye pattern from the heating of the valve).  You also get more soot in the exhaust instead of grey lead deposits.
The main potential issue is with the fuel system related to temperature and Mogas's higher vapour pressure (lower boiling point).  If your plane has a fuel pump and it gets really hot under your cowling, it's strongly recommended to add a cooling shroud for the fuel pump (I recently added one to my plane to alleviate problems in really hot weather, where I could tell I was getting fuel pressure fluctuations after landing). It's a bigger problem for fuel pump systems than gravity feed because the pump's suction is effectively raising the altitude, as far as the fuel being pulled into the pump is concerned, and the fuel will boil more readily at the pump inlet. Gravity feed doesn't have this problem.
You can actually run high compression 100 Octane non-turbo Lycs like the O-360 on Mogas (I was in a glider club with thousands of hour operation on it with O-360s) and there is no issue with detonation, and in Canada you can even run engines like the supercharged R-985 on Mogas, on commercial operations even (some bush operators use it).
The above assumes the fuel is alcohol free. You can't legally use car gas with ethanol under the STC anyway, and if you have a homebuilt where you can use whatever you want, and want to use fuel with ethanol, then you have to make sure that all the rubber components in the fuel system, including the carburetor float valve seal, are alcohol compatible. This is possible to do.
Finally, if you are getting Mogas yourself from a gas station, make sure it is alcohol free and test it yourself (a simple test using water) to confirm it is alcohol free.  If you're buying it from an airport, that's not a problem.

For any certificated aircraft engine, the type certificate will specify the required fuel. If the TC specifies AVGAS, using MOGAS will require an STC for that engine.
Developing a MOGAS STC for an engine is a complicated and expensive effort, so you're realistically limited to purchasing the rights to an existing STC. If there isn't an STC for your engine, you're likely out of luck.
The two most common STCs for GA piston engines are available from EAA and Petersen Aviation. Check their web sites for a list of engines covered by their STC.
Once you purchase the STC, it will include the installation instructions outlining the necessary modifications for your engine. In many cases, it's nothing more than placards and a flight manual supplement.

This doesn't really answer the question, the OP asked what modifications are necessary, not if they need an STC or how to get one...

The question is quite broad as the solution is dependent on the specific engine model. The STC is what defines the necessary modifications. And installing an STC is a modification to the engine.

I don't think it would be impossible to answer "what is needed to change from avgas to mogas" without being specific to a model. You can generalize things like re-jetting the carb, may require a new pump, valve seat issues, etc.

'Off the top' (with the usual risks associated with human memory): A few years ago, the engines of a couple of DC-3s based in Switzerland and flown for sightseeing tours were modified for leadfree 95 octane gasoline. The main modification was fitting specially designed cylinder heads...


text:
Why is air accelerating over the wing surface?
I know that there are dozens of questions about lift generation here but after reading them I still don't understand everything. My question is: why does air accelerate over the (upper side) wing? I know that it accelerates because there is pressure differential etc. but why wouldn't the air just flow over both sides of the wing with equal speed?

The Abdullah's answer is correct to it's level of approximation, but I'd like to expand on why the pressure is reduced on the leeward side.
As the air encounters the leading edge, it is pushed out of the way. Due to first law of motion, it would like to continue moving outward from the wing and avoid the area just above the wing. But besides inertia, air also has viscosity, which prevents sharp changes in air velocity, so the incoming air trying to pass high above the wing drags the air near the wing along. But when the air just above the wing is pulled out aft, there is shortage of air just over the wing, which means low pressure.
This low pressure causes the air bend around the wing, and since it pulls air from all sides, accelerate as it enters the low pressure region over the leading edge and decelerate again as it leaves it over the trailing edge.
Without viscosity (e.g. in liquid helium) the pressure would not be reduced, because the oncoming fluid would just continue straight over the highest point and the area over the receding part of the upper surface would be filled with stagnant fluid moving with the wing. In fact that's exactly what happens in stall – as the curvature increases (due to higher angle of attack), at some point the viscosity is no longer enough to keep the air moving, the area over the wing gets filled with air just whirling around and not moving away, so there is no longer shortage of air, the sucking of oncoming air stops and the generated lift rapidly decreases – just the lower surface still generates some.

The common sinktop aspirator helps explain this one.  Moving viscous fluid (water) pulls some air along with it, creating lower pressure in the air tube.  Same thing with the wing.  Important to see the wing in motion and proper AOA are needed for lift. Still wonder about liquid helium at a much higher speed, but, oh well, no practical application (yet).

hmm, liquid helium. interesting +1.  lack of viscosity does also mean zero friction.

Air accelerates over the upper side. The reason is simple:
As the wing - or anything else in air - moves, it creates high pressure at the front and low pressure at the back. The air flowing around the wing gets sucked into this low pressure region, and the suction accelerates it. (It will slow down again at the end of the low pressure zone) But the downturned trailing edge means that only the air coming over the upper surface can access this suction. The air flowing over the bottom has no idea of the suction zone above.

The "conventional wisdom" for the layman claims that the accelerated air moving over the top of the wing is what creates the low pressure, not that the low pressure zone is what accelerates the air. I've been reading answers here for years and I'm still a bit lost on that...

@FreeMan It's a chicken or egg question. They go hand in hand or none at all (for subsonic).

@FreeMan, it makes a bit more sense to say the lowered pressure causes the increase in velocity, though it's really the pressure field that causes both, and the pressure field looks like it does because of inertia and viscosity.

Note that in ‘ideal fluid’, the pressure behind a moving object is just as increased as ahead of it, so called pressure recovery. It is only due to inertia and viscosity that in real fluids the pressure recovery is imperfect and leaves the pressure behind lower than ahead.

When the wing moves forward in space it displaces a lot of air and creates a low pressure vacuum-like area in its wake. The gradient between high and low pressure is actually the most intense at the top of the wing, which causes the air to accelerate rapidly from high to low pressure.

What is the green dot supposed to represent?

It’s supposed to be the general area where the pressure gradient is the most extreme

From a layman’s point of view:
As far as lift generation, it is more precise to say that the lower static pressure generated perpendicular to the chord line of the wing is created by an increase in velocity of the air molecules instead of saying that the acceleration is created by the lower pressure. The acceleration of air molecules is greatest on the side (Upper or lower) of the wing with the greatest curvature. Basic aircraft wings are usually curved more on the upper-side of the wing than it is on the lower-side. This curvature creates a greater distance to travel in the same amount of time. Hence, the molecules are accelerated.
Think of it like a marching band or a column of soldiers marching. When soldiers or musicians have to march, they do so at the same speed. Both the cadence and the length of everyone’s steps are identical. When soldiers or musicians have to turn their column to march around an object, the individuals at the outside of the turn will move at a faster pace than the ones on the inside by lengthening their strides. If the turn is very sharp (like a 90° turn), the individuals on the inside of the turn will slow their pace by shortening the their strides. They do this because their is now a difference in the distance they have to travel in the same amount of time. Because there is a greater distance on the outside of the turn, there are fewer individuals per square feet of space on the outside of the turn than the amount of individuals on the inside. But since the column is not stopping, the file of individuals will continue to build up on the inside of the turn while waiting on the individuals on the outside of the turn to catch up. The column viewed from above will look like an accordion or a spring bent in the middle: a lot of material on the inside of the bend; very little material on the outside of the bend.
Let’s transfer this analogy to air molecules that are stationary relative to an airmass. The wing is actually moving through the airmass instead of the airmass moving over the wing. Either way, the side of the wing that makes the molecules move the furthest will temporarily have a lower static pressure and a higher velocity as the same mass of air on the other side of the wing. The lower static pressure creates a vacuum along the curved side of the wing. The molecules that were adjacent to one another at the wings leading edge, before encountering the wing, do not have to necessarily meet at the trailing edge. The average static pressure difference along the wing is enough to create this vacuum. The dynamic pressure of the air mass build up on the other side of the wing will also contribute to lift and increase with angle of attack.

The air flowing over the wing reaches the trailing edge long before the air flowing below it that encountered the leading edge at the same time. That is, the speed difference is much bigger than could be explained by different path length.

Flat plate generates lift exactly the same way as typical wing, except it forms a separation bubble behind the leading edge almost immediately, which then leads to early stall. Obviously the upper and lower surfaces of a flat plate have the same length in the flight direction.

Thin cambered wings like most birds and early aircraft have also have the same or almost same length of the upper and lower surface in the flight direction, yet the curvature means the effect on upper and lower surface are exactly opposite, lowering the pressure and increasing speed on top, but increasing pressure and lowering speed on the bottom.

It does not really make sense to say whether the lowered pressure causes speed increase or the other way around, they are simply tied together by conservation of energy. Inertia and viscosity is closest to what ‘causes’ them as far as it makes sense to say that – physical laws work both ways.

@JanHudec - True, Bernoulli’s Principle based on conservation of energy is the exact reason for the system to works. Although Bernoulli postulated the principle based on the conservation of energy to work for incompressible fluids. I figured that was getting too far in the weeds for a layman explanation. Although, feel free to expound upon the exact reasons for BP to work in a posted answer.

No, Bernoulli's principle is not the “reason” the system works. It is part of the reason, but the reason is only the complete set of Navier-Stokes equations (which of course includes conservation of energy). The reason Bernoulli's principle explains nothing is that it is just one equation with three free variables. Well, you need two more equations to solve anything – and note that there is no other equation that would fix velocity here, they all fix the pressure (field – you need to calculate it at all points).

@Dean F. Your 3rd paragraph is actually pretty good.  Alas, the first repeats a misunderstanding that "moving air creates lower pressure" when it's more like "pressure differential creates moving air".  The "aspirator" effect on the upper wing seems more Coanda.  But the moving wing striking stationary air could be your entire answer.  In reality, on the upper wing, net lift is created (at adequate airspeed) because the wing zips by faster than upward deflected air can return to the surface.  For every molecule pushed up by the leading edge, 10 are trying to return, a mechanical advantage.

This helps explain amazing lift/drag ratios.  Jan's explaination could further be investigated to see if very light molecules, such as hydrogen or helium, produce less lift at a given speed than Oxygen, Nitrogen, or (for that Mars helicopter), CO2.  Also, a "layman" discussion could include bottom lift, which is essentially "surfing".


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Do vapor clouds increase the radar scross section of an aircraft?
The F-22 is known for its stealth capabilities, which is mostly achieved with an extremely low RCS. Due to its high maneuverability we also see this plane often creating extreme vapor clouds while maneuvering:

Source: Wikipedia
We know that weather radar can detect clouds, so do such vapor clouds increase the RCS of the airplane?

The RCS seems like a simplification beyond what's reasonable here. A typical weather radar will probably ignore clouds moving at Mach 1, on the reasonable assumption that they're likely noise signals.

I'm not referring to weather radar, but rather to radar designed to track aircraft. I gave the weather radar example as evidence that condensation reflect some bands of radar. Do any aircraft-tracking radars look for this type of condensation.

Additionally, a condensation cloud moving above 50 knots might be the perfect signature to detect an inbound F-22. Maybe AA radar systems should look in the weather radar bands.

I think a better way to phrase this would be "do vapor clouds increase the likelihood of detection" rather than asking about radar cross section, which is fixed.

@GdD: I am actually specifically interested in the radar properties, but any answer which addresses your more general question would be of interest to me and warrant an upvote.

As with most things involving the military, the latest generation of radar detection is classified, and no one really knows all the tricks it uses to work.
However, ignoring the newest bells and whistles let's answer your question with simple radar implementations.
At it's core, radar is a broadcast of an electromagnetic pulse that bounces off anything which reflects it. This reflection is then picked up by a receiver, and after some computer math you get radar predictions.
So the important question to ask, is what band of electromagnetic radiation is being used, and will that particular band of radiation be deflected by cloud vapor?
Most aircraft detection radar uses radiation in the low frequency areas. As you can see on the chart below, long waves are also called "radio waves" is the normal frequency.

This is also what weather radar uses, so it's quite obvious that yes the vapor cloud of the plane will deflect the radio waves. In fact most ham radios operating off similar frequencies rely on the deflection of clouds/upper atmosphere imbalances to communicate with other radios without having a line of sight.
However this is the interesting part. The vapor cloud a jet fighter produces doesn't normally last that long, and when the receiver starts getting the strange data of a small cloud appearing and disappearing it's up to the radar operators/manufactures what to do with this data.
Do you write it off as noise? Or do you say "hey this cloud is moving at mach 1, and is appearing and disappearing in a predictable flight path, we should probably shoot a missile at it."
I'd imagine the military would chose the latter, and I would think the military of any powerful nation would learn to exploit these vapor clouds.
However again that's kind of classified information, so I'm really guessing at this point.
I could end the answer here, but I want to explore another aspect of next gen radar which is the use of infrared radiation. Also called "heat" radiation.
Infrared radar uses a receiver to detect objects in the sky that are emitting heat. Jet engines obviously leave quiet a bit of heat in their wake so this works pretty well.
Now can the vapor cloud diffuse this type of radiation? Maybe, but probably not.
I say maybe because I've never been able to measure the temperature of a jet's vapor cloud, but I'd imagine it's pretty hot. However if you want to make the argument that it's only slightly above ambient temperature then maybe this will temporarily help mask the aircraft's heat signature.
If though you think like me that the vapor is very hot considering the extreme pressure the air just went through to make the vapor cloud in the first place, then this will work against the aircraft to expose more heat to ir detection.
So to answer your question, yes this could cause a problem with radar detection, however I hope that anyone who puts billions of dollars into building these aircraft know about this limitation and inform pilots not to do a vapor causing maneuver within enemy radar when stealth is needed.


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Why don't modern fighter aircraft hide their engine exhaust?
In many photographs, the F-4's unique geometry hides one or both engines. I've been told that this is one of the terrific accidental features of the F-4, as it would help shield the hot exhaust from sensors used on heat-seeking missiles.
Is it true that the F-4 was harder to target with heat-seeking missiles due to the shape of the empennage? If so, then why don't modern aircraft use a similar design?
Example images:

"Why don't modern fighter aircraft hide their engine exhaust?"  But they do.  IR hiding is part of stealthiness.

There are a few which do (none of them in production, though) and the reason is the added weight and restrictions in varying nozzle geometry for best efficiency.
The tail arrangement of the F-4 is the result of its heritage. Early McDonnell jets all had the fuselage extended past the engine exhaust in order to shift the engine mass forward, near the wings, so the internal ducting could be as short as possible while the long fuselage held the large amount of fuel required for their initial design as long-range escort fighters. Originally the engines were placed in the wing roots (F2H Banshee) and moved into the fuselage as wings became smaller and thinner while engines grew in size.
Compare the XF-88, the F3H of the Navy, the F-101 Voodoo and the F-110, later to be renamed F-4, and the similarity should be obvious. Other manufacturers like Northrop with their the F-89 Scorpion used the same layout. Like all earlier models, the initial designs of the F4H (the F-4 in the old Navy designation system) used a straight tail. To be fair, at this time IR guided missiles were in their infancy and a low IR signature was not part of the requirements.

XF4H-1 wooden model (picture source)
The later addition of dihedral to the outer wings and anhedral to the tail was for aerodynamic reasons, not to improve IR signature.
NASA's history pages report that

the […] high position of the horizontal tail in combination with the wing-shape parameters led to undesirable nonlinear pitching-moment characteristics at high angles of attack. The large anhedral angle, or droop, of the horizontal-tail surfaces greatly improved the pitching-moment characteristics, as well as increasing directional stability. To achieve the proper balance in dihedral effect for the integrated aircraft configuration, however, a large positive dihedral angle was incorporated in the outer panels of the wing. In addition, the wing dihedral elevated the wingtip vortexes relative to the horizontal tail and further improved the pitching-moment characteristics of the aircraft.

The biggest threat using IR targeting are small, shoulder-launched missiles which target the airplane from below. The F-4 engine and tail arrangement will do nothing to hide its IR signature from them. There are modern fighter designs which hide their IR exhaust, and they place the exhaust on the upper rear fuselage for the reason outlined above.

Top view of the Northrop XF-23 (picture source). However, using a rectangular duct for high-pressure flow requires much more mass than a round duct. Also, optimizing this duct for afterburner operation and thrust vectoring is much harder than with a round duct right at the end of the fuselage.

The heat-seeking missiles of the time when the F-4 entered service were fairly limited compared to newer designs, and had to be targeted at an angle where they had a good view of the tailpipe of an aircraft. This changed somewhere around the late 70s when all-aspect missiles were introduced, allowing aircraft to be targeted from other angles as well.
I've never heard the claim that the design made the F-4 more difficult to target, and I doubt that this is true. Nothing is done to hide the IR energy radiated by the exhaust in any way, and the aft end of the tailpipe is visible for anyone with an IR sensor to see.

That, and the position of the elevator would have guaranteed it gets quite toasty, causing it to emit thermal (IR) energy. So, it likely made the F-4 easier to target, not harder.

No.  The empennage on the F-4 was never laid out in that manner to shield against IR guided missiles tracking it not could the design aid in doing so.  Like the increased dihedral or the outboard sections of the wing the severe anhedral angle of the tailplane is more or less a cheap patch for poor aerodynamic design. The 23° anhedral to the tailplanes were added as a compromise to provide for better control authority at high AoA without requiring a major structural workaround to keep the tailfins clear of hot engine exhaust.  You will notice early mock ups of the F-4 had no anhedral angle to the tail plane.

Is it true that the F-4 was harder to target with heat-seeking missiles due to the shape of the empennage? If so, then why don't modern aircraft use a similar design?

I have no comment on the ability of the tail design making the aircraft more difficult to target with heat seeking missiles but I can give a few educated guesses on why this tail design is not often repeated.
The steep downward droop of the stabilizer implies it is producing a downward force to hold the nose up rather than contributing to the lift.  Wings on airplanes have this V shape so that the vector of the force the wings produce is upward and inward.  Should the plane roll then the wing that drops has more vertical force than the opposite wing, these forces are equal only with the plane level.  This keeps the plane on a level flight naturally.  An inverted V tail can achieve this same self leveling only if the forces it produces are now pointed down.  If the stabilizers were contributing lift then a roll of the plane would produce more lift on the wing that was raised in the roll, this then produces more lift and a positive feedback on the roll making the aircraft inherently unstable.
Using stabilizers that produce a downward force instead of lift is inefficient.  It is producing drag on the craft with this force and not contributing to the lift, meaning the wings need to counteract this downward force with more lift, and this lifting force not only must lift the craft but counteract the downward force of the tail.
This was likely an engineering compromise as there is no inherent reason that the tail cannot also contribute lift.  There was no doubt a center of gravity problem on the wing placement and it was easier to have this less efficient tail than to redesign the entire airplane.
So, one reason this is not repeated often is because it is an inefficient tail configuration.  Another reason for not having an inverted V tail design is that with modern computers it is possible to achieve stable flight without any canting of the wings and control surfaces, this brings higher performing aircraft.
In high performance aircraft like fighter jets the engineers will want to remove drag where they can.  The canting of wings to get an inherently stable configuration means that there is an always present inherent drag.  On aircraft that carries passengers this inherent safety is an acceptable compromise as it gives a failsafe for a computer failure.  On a fighter jet this failsafe is removed because the gain in performance is vital.  There will be redundant computers to provide some level of a failsafe against flight control computer loss, just not in the wing and control surface configuration.
This is an inefficient design made no longer necessary with modern flight control computers.  I've seen this kind of tail on military drones before.  This also appears to be an engineering compromise in getting an existing drone design to carry heavy observation equipment in it's nose without having to redesign the entire craft or make large changes to the flight control computer.  With bigger wings, an inverted V tail, and maybe a more powerful engine, they can get something flying with the intended payload quickly.


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Manual or other information regarding Kollsman Instruments B40331-10-276 altimeter
I just purchased a used altimeter from eBay because it'll look pretty on a shelf, and I may add a computer interface to it. However, I need help finding information on it.
This (from what I've been able to gather) is a Kollsman Instruments model B40331-10-276 altimeter. It's serial number 575A. There is a port on the back with a red plastic plug, which is obviously the static pressure connection (NB: If I try real hard I can suck myself up to 8000 feet). There is also what I would call a "cannon plug" with 19 pins.
Label on the back reads:

ALTIMETER, PRESSURE CORRECTED TYPE INTEGRALLY LIGHTED 5VAC 0.68 AMP RANGE -1000 to +50000 FEET FAA TSO-C10b KOLLSMAN INSTRUMENT CORPORATION ELMHURST NEW YORK

Primarily, I want to know the specification of that electrical port - pinout, voltage/current ratings, protocol descriptions, etc. A bonus would be a repair/calibration manual with all the details. Perhaps this is a standard avionics connector, so a link to a standard would work.
Of course, if this is identical in all respects to another model, and there is information on that model, please share.
What are the dimensions of the threaded static port as well?
Here are some photos of the instrument:

Credit: My own photos
I believe my biggest and only leap was figuring out where the dashes went in the model number...

Side question: Is it safe to carefully disasseble the instrument without damaging it or injuring myself? I do not need to keep any kind of warranty or fit-for-use, and I doubt it could even qualify considering how I obtained it anyway.

Stretch bonus: Can I trace where this came from?

I did find this standard, but I think it would set general performance minimums that need to be net by altimeters in general, as opposed to how they actually must operate or interface (to some extent). https://www.sae.org/standards/content/as8009c/#:~:text=Pressure%20Altimeter%20Systems%20AS8009C,a%20function%20of%20atmospheric%20pressure.

Well, you are certainly not going to injure yourself by disassembling the instrument, unless you are extremely inept at using tools and stab yourself with a screwdriver etc -- it's not a like a bomb waiting to blow-- as far as damaging it, someone else could probably speak to that better, but seems to me if you are careful it should all work out ok--

That's enough for me to proceed with something, thanks @quietflyer.

I wouldn't take it apart. Most of it is encoder output (see below)  and you should be able to find power and ground with an ohmmeter.

Undoubtedly an encoding altimeter. Ten pins are the encoder output. This is Gillham coded, a 12 bit Gray code identifying altitude in hundreds of feet. D4 is needed above 30750ft which makes ten pins. Power and ground are two more. Dimmer, serial data and/or strobe possible.

Sample transponder connections:

Sample startup operation.

Electrical Connections: Use the 15 pin socket provided with the unit to
make a wiring harness. The harness should have 14 wires: 10 for altitude
data and one each for strobe, serial data, power, and ground... Most transponders have available switched power (A+) or a direct
connection to the aircraft avionics bus may be made. When a connection
to the avionics bus is made, a 2-Ampere circuit breaker should be
installed. Connect pin 6 to ground if the transponder does not have a strobe connection... Pin 6 of the encoder connector is the strobe line.
Logic low (less than 1.2 volts) on this pin enables encoder output.
When power is first applied to the encoder, all of the output data
lines will pulse high/low. Each data line will then go high and low
individually until all of the lines have been pulsed. This action is normal
and serves as a diagnostic tool for the installer to use in verifying the
encoder output and the harness on a line-by-line basis.

Yours may not do this. You can order a manual at Carp Ind. Search "B40331". No description as to service, operator or repair manual.
Kollsman is now a subsidiary of Elbit.

Any idea what the signaling is? Common emitter/pull to ground (e with pull up) or voltage levels, etc?

@Steve Logic low is less than 1.2v. I don't have docs but logic high at 5v would be likely.

I'm running out of time and can't get back to this project, so the bounty is yours!


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Which amount of fuel is important - mass or volume?
I am wondering which information of fuel amount is the significant one. Because all light aircraft have fuel quantity indicators scaled in litres or gallons, so in a unit of volume. But I heard that in airliners and other bigger planes have fuel quantity displayed in kg or lbs. So which unit is "correct" and a running engine at constant power setting needs constant amount of fuel in kg or litres? Please help me out with that and please explain also the importance of changing fuel density with temperature (and maybe with some other factors?).

Strongly related to On what basis is the weight unit of the FQIS selected by airlines of various countries?. Mass is potential energy, what means for the crew is energy to run the engine, not volume.

Both. Mass is used for weight and balance and total BTUs in the fuel for range. Volume (based mostly on temp) is used to see if it will fit into the volume of the tanks and to pay for it.

Mass is more useful, but volume is easier to measure.
Mass is needed for weight-and-balance calculation, and the energy stored in the fuel is also proportional to mass, so when the engine is set for cruise parameters, it will burn roughly the same mass per unit of time every time, making it more useful for range calculation too.
However there is nothing that could directly measure mass of the fuel, while the volume can be measured by a simple float in the tank. Therefore

For GA planes you have indicator in volume, and assuming the standard density is usually good enough.
Transport aircraft have advanced sensors that can estimate the density as well and indicate fuel mass.

See also How does a fuel density sensor work? (densitometer, cadensicon) and How is fuel mass measured in airliners?

Volume limits how much fuel a given tank can hold; on a warm day with warm fuel, "full tanks" gives you less fuel - i.e. less mass and therefore less range - than you'd have with cold fuel.

@RalphJ, yes. However in larger aircraft you always load the fuel you need for the trip plus appropriate reserves, so you almost never reach the volume limit.

Kilo’s are important. Energy contents is given in kJ/kg, so the weight of the fuel on board determines the range of the aircraft. For commercial aviation, this precision is imperative.
Liters are used in cars and small aeroplanes because they are easier to measure. But on warm days a warm liter of fuel weighs less than a cold liter - volume measurement introduces the variability of expansion.
It is possible to directly measure the kg/sec of fuel that is taken on board, it is simply that the mass fuel rate meters are more expensive than the volume ones.

this. Mass determines how much fuel you have. Volume in liters or gallons is just a convenient way of measuring it but is not nearly as accurate. Density change due to temperature can skew the measurement by several percent. For example, 40C avgas is a full 10.5% more volume than -40C avgas of the same mass.

Or more precisely: how much energy you have... both weight and volume are perfectly valid when measuring how much of a substance one has. Energy is of importance in aviation.

@Jpe61 True, and that is why weight is the gold standard. Volume expands and retracts as a function of temperature, weight remains constant.

@Jpe61 "both weight and volume are perfectly valid when measuring how much of a substance one has" is a false statement.

Lol. Go troll somewhere else.

Its all about the ease of measuring out the required fuel.
Before departure the pilot will need to calculate his take-off weight. eg if you have a plane with a max take-off weight of 300,000kgs.. the weight of the fuel, the plane and the load cannot exceed this. Assuming the weight of the plane and load is 250,000kgs.. this means that there is space for 50,000kgs. If this is not enough then load has to be removed to allow the weight of the fuel required. Sounds complex but not really when you do it everyday.
The problem shows up when you have to pump the fuel into the tanks. While it may be possible to weigh the bowser (tanker) and derive the fuel uplifted by reweighing it after the plane has been fuelled, its a bit cumbersome. Also for the amount of fuel that a widebody can uplift (170,000kgs on a good day for a B747-400) it is pretty impractical. Also most airports use hydrant systems for refuelling where there is a fuelling port in the ground at the parking stand and all the fuelling truck does is meter and pump it into the plane.
Measuring fluids however is much easier and has been in use for a long time. How it works is as follows.

The Specific gravity (SG) on the day needs to be known. The SG is the ratio of the weight of the liquid compared to the weight of 1litre of pure H2O which is also 1kg. For this example lets use an SG of 0.779. In this case one litre of fuel will equal 0.779kg. The  density varies with temperature and the fueller will usually check it before fuelling using a density meter/hydrometer (like used to check battery acid).

Assuming the pilot requires 50,000kg of fuel. To convert 50,000kgs into litres, we need to divide the weight by the SG (50,000 / 0.779). this equals 64,185 which is the amount in litres. Most airliners have a fuelling panel where you just set the amount required in kgs (or Lbs) but the calculation behind the automation is the same. (note:A real life situation will have some fuel already in the tanks)

Upon completion of fuelling, the fueller will typically handover a fuelling receipt with the uplift amount in kgs. Here the pilot or engineer will convert this amount into kgs and factor in the fuel which was already in tanks. The final number is what the pilots have planned for and expect for the flight.

It seems pretty hit and miss and in real life the numbers are not really accurate. It is common to have a few hundred kilos more on an aircraft like the 744.


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What is the purpose of attaching a flat plate to the rudder trailing edge?
These are photos of Tecnam P2006T rudder trailing edge. Why it has such flat plate mounted at the end of the rudder?

What seems be the case here is that a truncated trailing edge has a flat plate riveted on (called a double Gurney flap). This places the plate perpendicular to airflow (more or less).  This, in turn, has the effect of increasing air pressure on whichever surface of the rudder is deflected into the airstream, giving a similar effect to increasing rudder area - but without the added weight of extending the trailing edge of the rudder.
Since weight in the tail is generally bad - because of the moment arm from the aircraft center of mass, a kilo added to the tail requires five kilos or more in the nose to return to correct balance -- this is probably done mainly as a weight saving on an aircraft that (as a twin) needs good rudder authority.  As a bonus, it reduces the amount of deflection required for a given yaw force, which makes trim inputs more effective.

It's a double Gurney flap, but I'm not sure how it helps, here.
Another example:

The Eurocopter AS355 TwinStar helicopter uses a double Gurney flap that projects from both surfaces of the vertical stabilizer. This is used to correct a problem with lift reversal in thick airfoil sections at low angles of attack. The double gurney flap reduces the control input required to make the transition from hover to forward flight.

In the context of aircraft, it's misleading to call this nonmoving surface a flap, of course.  But the term and the concept came from "hey, Billy Joe, let's rivet this on and see how she runs" motorsports, a culture that wasn't fussy about nomenclature.

Well done! Some information in this pdf.

The Tecnam P2006 is a twin, so they may have decided to have a bit more rudder authority for one engine out flying.

First, since it doesn't move, it's a bit silly to call this a flap. Second, thick trailing edges on control surfaces improve centering, so there is a steeper hinge moment gradient near zero deflection. A moveable T-shaped strip was tried out by Doetsch on the Gloster Meteor in the early Fifties, predating the work of Gurney. By making the strip moveable (shifting between only left and only right) the rudder trim was markedly improved.

the gimmick seems to be to have the strip as wide as the turbulent boundary to avoid significant increase in drag.  As flaps improve lift coefficient, the term is accurate.  Putting one right at the end would improve yaw stability, and, as said, improve both low (rudder) AOA response and high AOA authority.

Now I wonder when the the race car drivers will start using (fore and aft) rudders to help them turn.  Gurney actually made it as an improved spoiler.

Here is another consideration.
At the aft end of an aerodynamic body, we taper the body so the streamlines in the air flow over it do not separate, because of the flow separation drag penalty.
But in doing so, we increase the length of the body's tail end, which increases wetted area drag.
There then comes a point where truncating the fuselage profile (so as to minimize wetted area drag) is balanced by the creation of separation drag i.e., a "crossover point" exists where we can truncate the profile and not pay a penalty.
Note that several years ago, VW built a prototype ultra-high-mileage car with a teardrop shape- but with a blunt, chopped-off tail. The designers had discovered that extending the tail taper (making the vehicle longer) did not reduce drag enough to be worthwhile, and so they determined where that crossover point was and chopped off everything aft of it.

Yes but if you look at the photos, they don't simply show truncation.  They show that a plate is attached at the trailing edge of the rudder to increase the width of the trailing edge of the rudder.  Most clearly visible in the lower photo.

@quietflyer Actually, look again at the photos.  It looks like there's a truncated trailing edge with a plate riveted on perpendicular to the direction of flight.

Yes, that's what I see too, maybe I didn't describe it clearly enough.

This truncation is called a Kammback after its 1930's inventor.  But it doesn't apply to this question.


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Are return springs on a carburetor throttle mandatory or not?
In many GA aeroplanes throttle control is connected mechanically to the throttle of carburetor via a cable. I read in some AFMs that in case of a cable failure, return springs will open the throttle so an engine will be at full power.
Is it mandatory to have those springs installed (a certification requirement or something) or it is optional? I'm asking about EASA regulations, but a reference to FAA regulations will also be helpful.

Which AFMs?  I've never seen that myself.

e.g. Aero AT-3, PS-28 Cruiser

From the airplanes you mentioned, that's sounds like it's maybe an Eastern European practice.  I've never heard of any regulation requiring throttle springs in North America, but I can't speak for EASA requirements.

You might be interested in https://law.justia.com/cases/oregon/supreme-court/1978/577-p-2d-1322-6.html. As I remember (50 years ago now), Piper issued an AD requiring a spring be put on the carburetor. In the accident, what happened is that the engine quit when the carb heat control was pushed in to get full power.

@Terry Couldn't find an AD that requires a spring on Cherokees in the database.  That crash seems to be mostly about carb icing.

The FAA doesn't require it. Some carb manufacturers may have them but I've never seen them used. You can get return springs for Rotax engines but only for non-certified aircraft and then again only to prevent throttle creep.

The FAA doesn't require it, but some carburettor manufacturers may have them. You can get return springs for Rotax engines, but only for non-certified aircraft and then again only to prevent throttle creep


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Does low pressure induces high velocity or high velocity induces low pressure?
Does low pressure induces high velocity or high velocity induces low pressure? I am wandering what is the cause and what is the result. I mean i.e. Bernoulli principle or situation in the core of a vortex.

are you asking about Bernoulli's principle or something else?

what are you asking here? could you be more specific, velocity of the airplane ot the wind around.

My fault, question edited.

@Konrad this one may be migrated to Physics Stack too, but is a great fundamental building block question.  High air velocity is caused by pressure differential between higher and lower pressure.  A fast moving air stream of air (or water) will pull air away from a surface, creating an attraction of the surface to the airstream (Coanda effect).  The latter seems to explain lift from airflow over the top of the wing, while lift from the bottom is action/reaction of the (moving) wing pushing air down.

And what about i.e. wingtip vortex? There is a low pressure in a vortex core and higher and higher pressure if we move away from the core. In this case isn't (angular) velocity a cause of pressure drop in a core (highest angular velocity in a core and slow decrease if we move away from a core)?

@Konrad  vortexes are interesting in that the rotation does carry angular momentum but only in the plane of rotation. (not like a tornado)  Pressure can equalize (from top or bottom) after the vortex drifts away from the wing, but the rotor motion will take longer to dissipate (from drag).

the walls of a tornado can act as a pressure "barrier" (by rapid rotation), but lower pressure is maintained from the top, and the ground acts as a "seal" from the bottom.

@Konrad, the downward velocity in the wake is due to the work done on the air by the wing, so it does not reduce the pressure. As the air leaves the trailing edge, it has additional downward velocity compared to the free stream, but is at ambient pressure.  See also https://aviation.stackexchange.com/questions/80119/why-high-air-speed-at-flat-surface-dont-always-produce-low-pressure?rq=1

… only as the wake interacts with the surrounding air mass and rolls to a vortex does the pressure gradient form that generates the centripetal force needed to keep the air rotating, and here Bernoulli's principle tells us it is accompanied by further increase in velocity in the core of the vertex. But the vortex exists because it has more energy than the free stream, not because of this pressure decrease.

Neither! The cause is wing moving through the air, and the effect is a fairly complex flow pattern around it that produces lift (and wake vortex).
We know that the flow obeys certain laws (that are largely averaging of the microscopic laws governing individual molecules). One of them is law of conservation of energy, which for fluids is known as Bernoulli's equation. But that's just one equation with many free variables, so alone it is not enough to explain anything. You need the complete set of Navier-Stokes equations to be able to describe the flow.
The equations are partially differential, and need to be evaluated for every point in space and time, which can only be done approximately and requires a computer.
There is only a few conclusions that can be made using conservation laws without this, the most important probably is the existence of downwash. The third law of motion tells us that if upward force, lift, is applied to the wing, downward force is applied to the air, and second law of motion tells us that this force accelerates the air downward. The boundary between downward moving air behind the wing and the still air outside the span is the wake vortex.
But again, neither is cause and effect. The laws of physics work both ways. They just tell us that these phenomena always occur together. But the cause is the situation. We just know that both or neither will occur.


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Why battery voltage is lower than system/alternator voltage
I’m a noob in electricity so pardon for my ignorance. Why the battery voltage is always lower than whole system and alternator voltage (considering light aircraft electrical system). E.g. In Cessna 150 system voltage is 14 V and battery voltage is 12 V, in C152 system and alternator voltage is 28 V and battery voltage is 24 V.

This is more of an Electrical Engineering question than Aviation, indeed the exact same thing can be asked about any automobile.
Both of the figures that you quote are 'nominal': The battery cannot be expected to put out a much higher voltage than 12v, so in reality, all systems will work fine down to about 10volts or so, though 'normal' voltage will be 12.5v for a reasonably new, modern battery in good condition.
Conversely, the battery itself requires a significantly higher voltage to charge itself, so the alternator needs to put out 13 to 14 volts, which gets rounded off to 14v for simplicity when talking "in general".
Nearly forgot - for some heavy duty systems, a 12v system is insufficient, so the battery is simply doubled up, so 12v nominal becomes 24 volt, etc., but with the same tolerances.

You should express the last bit in terms of wattage.  Going to 28v is mostly to allow a doubling of wattage capacity of the overall electrical system without having to make the wire sizes larger. Or if starting from scratch you can make the wires smaller.  You also get a bit less sensitivity to poor connections, especially with voltage sensitive circuits like those with variable resistors, while having to live with more demanding insulation requirements.  28 v has been settled on by the aviation industry as the best compromise for DC systems taking all that into account.

plus not all battery chemistries are 12 V / 24 V nominal. Ni-Cd and Li-Ion will have different nominal voltages but they are still designed to work on a 14 V / 28 V charging system

Indeed, the alternator on my Piper Cherokee is exactly the same as used on '60s Chrysler products.  If you have a more modern car and an OBDII reader, you can easily see the system voltages.  On mine, it's 14.4 volts when the system is charging, 12.8 down to about 12.4 when running off battery.  If it gets down below that, the alternator starts charging again.

@selectstriker2 Everything about aircraft design is extremely conservative for safety reasons. You are unlikely to find anything except Lead-Acid certified for a "old" design like a Piper or Cessna. (And of course Boeing learned about the consequences of battery problems the hard way, with the 787!)

If you think about it, if you want to push the electrons the wrong way through the battery, you have to push them harder than the battery is pushing back. That's why the alternator voltage is higher than the battery voltage.

@alephzero I think you'll find that it's more about cost for an STC in those "old' designs nowadays, rather than a safety requirement